This invention relates to a process for recovering metal values from a sulfide-containing material, and more particularly to a process for the recovery of calcium and sulfide values from a calcium sulfide-containing material, such as slag produced in a blast furnace.
Many processes for handling slag and like materials to recover calcium values have been advanced, but have met with limited acceptance. In one such process, slag (a CaS/Ca(OH).sub.2 mixture) is contacted with weak caustic solutions for a prolonged period of time at temperatures of about 200.degree.F. whereby a significant amount of the lime is recovered. The sulfur values, however, as sodium polysulfide remain in solution and are disposed of by passing such a solution including entrained ash as waste to disposal. In another process, slag is pyrolized in the presence of gypsum and controlled amounts of oxygen with sulfur values being recovered as sulfur dioxide contained in the off-gas. In such latter process, no provision is made for the separation of ash.
The capacity of calcium oxide as a sulfur acceptor has long been recognized in the metallurgical art, e.g. in the production, inter alia, of iron, copper and the like. Recently, such capacity has found applicability in fuel gasification processes, such as described in a brochure published by the American Chemical Society in 1967 entitled "Fuel Gasification" wherein calcium oxide in the solid state is used in a fluidized bed system. In U.S. Pat. No. 3,456,622 to Thornton et al. and assigned to the assignee of the present application, there is disclosed a process for removing the sulfur values from a flue gas using a solution of calcium carbonate. In order to permit such processes to be competitive, other than by legislative action, it is necessary to have an efficacious and facile process for the regeneration of the initial calcium compound from a sulfide-containing compound thereof.